T he Laborataory Sheep Colony is an NIH animal resource providing varied age sheep that meet specific year-raound requirements of the Clinical Hematology Branch, Laboratory of Technical Development, Pulmonary Branch, and Surgery Branch, DIR, NHLBI; and the Laboratory of Biomedical Sciences, IRP, NICHHD. Maintenance regimens in use have resulted in successful year-round breeding and production of varied age sheep. Practices that have contributed to reduction of undersired seasonal variables include: (1) continuos prophylactic immunization of all age animal groups; (2) accurate pregnancy diagnosis during first trimester using Doppler ultrasound: (3) monitoring of animal health using various diagnostic laboratory techniques; and (4) many husbandry techniques unique to this colony. Such practices have been cost prohibitive in commerical sheep flocks that result in inconsist availability and existence of varied states of health in animals delivered for laboratory use.